Angular 2 cache observable http result data [duplicate]

Answer 1

I think you should not do a fetch() in the constructor or any time in the lifecycle of angular. And as you say, ngOnInit does not work in angular services.

Instead we want to leverage rxjs to seamlessly pass us cached values through the stream – without the caller having to know anything about cached vs non cached values.

If a component needs a data, it subscribes to it, regardless if it is cache or not. Why would you fetch() a data that you are not sure it will be used ?

Cache should be implement at a higher level. I think this kind of implementation is a good start : http://www.syntaxsuccess.com/viewarticle/caching-with-rxjs-observables-in-angular-2.0

getFriends(){
    if(!this._friends){
      this._friends = this._http.get('./components/rxjs-caching/friends.json')
                                   .map((res:Response) => res.json().friends)
                                   .publishReplay(1)
                                   .refCount();
    }
    return this._friends;
}

I am not sure it is the best way, but it is easier to maintain because it has a single responsability. Data would be cache only if a component subcribes to it, no matter what/who/which component needs the data and is the first to need it.